Proton exchange membrane water electrolysis (PEMWE) is a promising way to produce green hydrogen utilizing intermittent renewable energy. While Ir is the only catalyst with good activity and durability for PEMWE, Ir is the rarest material on earth. Ir minimization is crucial to expand the application of PEMWE. Previously, we reported ultrathin IrO2 nanoneedles (NN) for oxygen evolution reaction (OER) in PEMWE. Although IrO2 NN showed good electrical conductivity, its activity should be improved. Here, the OER activity of the NNs is further improved by depositing amorphous Ir atomic clusters (AC) on the one-dimensional NNs. The amorphous Ir ACs are highly active for the OER and the crystalline NN backbone aids facile electron transfers to the surface ACs. The het-erostructure of the Ir AC/NN catalysts decouple a trade-off relation between the OER activity and durability. PEMWE with the Ir AC/NN catalysts achieves a current density of 3 A cm(-2) at only 1.82 V and operates stably for more than 90 h, whereas pristine IrO2 NN and IrO2 particles synthesized by Adams-fusion method require higher potentials of 1.92 V and 1.97 V, respectively, at 3 A cm(-2).